diff --git a/sklearn/multioutput.py b/sklearn/multioutput.py
index cddbcbfff..accced9f4 100644
--- a/sklearn/multioutput.py
+++ b/sklearn/multioutput.py
@@ -194,7 +194,15 @@ class MultiOutputEstimator(six.with_metaclass(ABCMeta, BaseEstimator,
             delayed(parallel_helper)(e, 'predict', X)
             for e in self.estimators_)
 
-        return np.asarray(y).T
+        if y is None:
+            raise ValueError("The estimator predictions are None.")
+        if not y:
+            raise ValueError("The estimator predictions are empty.")
+
+        if isinstance(y[0][0], str):
+            return y
+        else:
+            return np.asarray(y).T
 
 
 class MultiOutputRegressor(MultiOutputEstimator, RegressorMixin):
